This invention relates to semiconductor substrates, and particularly to the improved configuration, and a method of fabrication, of semiconductor substrates which lend themselves to use in nitric compound semiconductor devices such as light-emitting diodes (LEDs) and heterojunction transistors, among other applications.
Nitric compounds such as gallium nitride (GaN), gallium aluminum nitride (GaAlN), gallium indium nitride (GaInN), and aluminum gallium indium nitride (AlGaInN) have been used extensively for production of semiconductor devices. Japanese Unexamined Patent Publication No. 2001-313421 teaches the fabrication of a nitric semiconductor region upon a silicon substrate via a buffer layer.
FIG. 1 shows a semiconductor substrate of the above conventional make. The semiconductor substrate has a silicon baseplate 1, a buffer layer 2 of aluminum nitride (AlN) or the like grown epitaxially on the baseplate, and a nitric semiconductor layer 3 of gallium nitride or the like grown epitaxially on the buffer layer. An additional layer capable of light emission is formed on the nitric semiconductor layer 3 for production of LEDs. An additional semiconductor layer is also formed on the nitric semiconductor layer 3 for production of heterojunction transistors or like controllable semiconductor devices.
The boundary between silicon baseplate 1 and buffer layer 2 forms a heterojunction, with a lattice and thermal discontinuity. For this reason, as indicated explanatorily by the broken lines designated 4 in FIG. 1, numerous dislocations conventionally took place across the buffer layer 2. The dislocations might also be termed line defects or dislocation lines. Oriented normal to the major surfaces of the baseplate 1, the dislocations extended into the nitric semiconductor layer 3, with a dislocation density of 5×1010/cm2 or more, which is detrimental to the performance of the semiconductor device. More specifically, in the case of an LED, the dislocations extended into the light-emitting layer to provide recombination centers that do not emit light and so decrease the efficiency of glowing. Also, in the case of dislocations contained in the semiconductor regions having controllable semiconductor devices such as high electron mobility transistors formed therein, the carriers were scattered by the electrons captured by the dislocations, lowering carrier mobility. The dislocations extended to the surfaces of the semiconductor regions having the semiconductor devices, causing abnormal dispersion of the electrode material on the surfaces, with a consequent decrease in voltage withstanding capability.